The need for a reliable and efficient strand detection system is well known in the textile industry. Many of the prior art devices use a light source and reflected light from the strand to actuate a light sensor and provide a strand presence signal. One such prior art device is U.S. Pat. No. 4,010,908 which discloses a guide for a filament or strand and a fiber optic system for supplying light to the guide and for receiving light reflected from the strand. Other examples of using reflected light to sense the presence of a strand are shown in British Pat. Nos. 1,124,590 and 779,548.
The strand detection system disclosed in commonly assigned U.S. patent application Ser. No. 940,068 filed on Sept. 7, 1978, for Sheldon A. Canfield discloses an optical sensor unit having a solid state light source and light detector. The sensor is focused at the outer periphery of a pathway through which the strand travels.
One problem with such a system has been the build-up of fuzz around the sensor that can disable the system.